Catalytic hydrocracking process with hydrogenation of the hydrocracked products



United States Patent O 3,203 89o CATALYTHC HYDRCRAZKENG PROCESS WITH HYDROGENA'HN 0F THE HYDROCRACKED PRODUCTS Vladimir Haensel, Hinsdale, lll., assigner to Universal @il Products Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. l, 1962, Ser. No. 234,683 13 Claims. (Cl. 268-58) The present invention encompasses a process for converting an aromatic-containing hydrocarbonaceous charge stock into lower-boiling hydrocarbon products by a method which involves the utilization of catalytic cracking in the presence of hydrogen. More specifically, the present invention is directed toward a combination process designed for the production of hydrocarbons, boiling within the normal gasoline boiling range, from hydrocarbonaceous material -boiling at temperatures exceeding the normal gasoline boiling range, which hydrocarbonaceous material is cont-aminated by the presence of exceedingly large quantities of nitrogenous and sulfurous compounds, and which contains high-boiling monoand polynuclear aromatic hydrocarbons. The process of the present invention is particularly adaptable to the conversion of hydrocarbonaceous material boiling at temperatures exceeding the normal middle-distillate boiling range, and affords unusual flexibility with respect to the quality and quantity of the lower-boiling hydrocarbon product where it may be desired to maximize the production of gasoline boiling range hydrocarbons, or middle-distillate boiling range hydrocarbons, or to produce an economically- `dictated balance therebetween.

Hydrocracking, sometimes referred to as destructive hydrogenation, involves the cracking of hydrocarbonaceous material in the presence of hydrogen and a suitable catalytic composite, whereby a change in the molecular structure is effected. Hydrocracking may be designated as cracking under hydrogenation conditions such that the lower-boiling products of the conversion reactions are substantially more saturated than when cracking in the absence of hydrogen, as in a thermal cracking process. Hydrocracking processes are most commonly employed for the conversion of a wide variety of coals, tars, petroleurn crude oils, heavy residual oils, heavy vacuum gas oils, etc., having as the object thereof, the production of a lower-boiling, saturated product; to a certain extent, intermediates which are suitable for utilization as domestic fuels, and heavier gas-oil fractions which find utilization as lubricants, are also produced. Although many of the present-day cracking processes are conducted on a strictly thermal basis, the preferred refining technique involves the utilization of .a catalytic composite, possessing a high degree of selective hydrocracking activity, and an atmosphere of hydrogen. The use of a catalytic composite affords the desired degree of control by which the cracking reactions are made more selective from the standpoint of producing an increased yield of normally liquid hydrocarbon product having improved chemical and physical characteristics. Furthermore, controlled or selective hydrocracking assumes greater significance in order to achieve acceptable stability and effective catalytic action over a prolonged period of time.

Controlled, selective hydrocracking is of particular importance when processing hydrocarbons and mixtures of hydrocarbons having normal boiling points at temperatures above the normal middle-distillate boiling range; that is, hydrocarbons and various mixtures of hydrocarbons having a boiling range indicating an initial boiling point of at least about 650 F. and an end boiling point which may be as high as about 1000 F. In the present specification, the term gasoline boiling range, is infice tended to connote a temperature range having an upper limit of about 400 F. to about 425 F.; the term middle-distillate boiling range, is herein designated to include temperatures above the gasoline boiling range, but not substantially in excess of about 650 F.; therefore, middle-distillate hydrocarbons include kerosenes, light gas oils, fuel oils, etc. Catalytic selectivity is required in order to avoid the usually experienced excessive decomposition of the normally liquid gasoline and middledistillate boiling range hydrocarbons substantially or completely into normally gaseous hydrocarbons, the latter generally considered as waste products. As a result of the excessive production of normally gaseous hydrocarbons, inherent in uncontrolled, non-selective hydrocracking, the volumetric yield of valuable gasoline boilingrange hydrocarbons is rapidly decreased to the extent that the process is not economically feasible. In illustration, it might be said that selective hydrocracking involves the splitting of .a higher-boiling hydrocarbon molecule into two molecules, both of which are normally liquid hydrocarbons boiling within the gasoline and/or middle-distillate boiling ranges. Thus, Iselective hydrocracking minimizes the removal of methyl, ethyl and propyl groups which, in the presence of hydrogen, are converted to methane, ethane and propane, the latter herein referred to as light paraffini-c hydrocarbons. Through the judicious choice of operating conditions and catalytic composition, primarily depending upon the physical and chemical characteristics of the hydrocarbonaceous charge stock, the production of the aforesaid radicals is 4controlled in order to produce acceptable yields of normally liquid hydrocarbons. Another disadvantage of non-selective hydrocracking, particularly in regard to catalytic processes, is the resulting rapid formation of increased quantities of coke and other heavy hydrocarbonaceous material which becomes deposited upon the catalyst and decreases, or destroys the stability and activity thereof to catalyze the necessary reactions in the desired, controlled manner. Furthermore, the deactivation of the catalyst appears to inhibit the hydrogenation activity thereof to the extent that .a significant proportion of the resulting lower yield of gasoline and middle-distillate boiling range products consists of unsaturated palaflswhereby the products are neither suitable for immediate utilization, nor for subsequent direct processing by catalytic reforming. Through the utilization of the selective hydrocracking process and catalytic composites of the present invention, a hydrocarbonaceous charge stock, which may consist entirely of hydrocarbons boiling .above the middle-distillate boiling range, is converted substantially completely into hydrocarbons boiling within the gasoline and middle-distillate boiling ranges, and a significant increase in catalyst stability is experienced.

Investigations into the problems attendant acceptable hydrocracking processes have further indicated that the presence of nitrogen-containing compounds, regardless of the precise boiling range thereof, results in the relatively rapid deactivation of the catalytically active metallic cornponent, as well as the solid carrier material which serves as the acid-acting hydrocracking component, and that the adverse effects of the high-boiling nitrogenous compounds are signicantly more deleterious than those which are caused by sulfurous compounds. The rapid deactivation of the catalyst appears to result primarily from the reac- F tion of nitrogenous compounds with the various catalytic components, the extent of such deactivation increasing as the process continues. As a result of the detrimental effect exhibited by nitrogenous compounds, certain hydroretining processing techniques have been suggested as a means of pretreating the charge stock for the purpose :of eliminating and/or decreasing the concentration thereof.

As hereinafter set forth in greater detail, these hydrorening techniques fail to pretreat, or clean-up, the charge stock to the extent required for an extended period of acceptable, stable catalytic activity. In addition to nitro- -genous compounds, the hydrocracking process is extremely adversely affected by the inclusion .of high-boiling monoand polynuclear aromatics within the pretreated charge stock.

A primary object of the present invention is to provide a catalytic hydrocracking process which results in the production of substantially greater yields of hydrocarbons boiling within the gasoline and middle-distillate boiling ranges. A related object is to provide a process utilizing particular catalytic composites and a reaction chamber arrangement which permits the utilization of a hydrocarbon charge stock containing lrelatively excessive quantities of high-boiling aromatic hydrocarbons otherwise having the tendency to cause the rapid deactivation of the hydrocracking catalyst. Furthermore, the process of the present invention makes possible the simultaneous production of gasoline boiling range hydrocarbons, kerosene fractions suitable as jet fuel blending components, and middle-distillate hydrocarbon fractions, all of which are substantially saturated.

In a broad application, the present invention relates to a process for converting a hydrocarbon charge stock containing aromatic compounds into lower-boiling hydrocarbon products, which process comprises commingling said charge stock with a previously hydrocracked product and hydrogen; reacting said charge stock and hydrogen at hydrogenation conditions and in contact with a non-siliceous hydrogenation catalyst, said conditions and catalyst selected to hydrogenate aromatic compounds Without substantial conversion of said charge stock into lower-boiling hydrocarbon products; separating the resulting substantially aromatic-free, hydrogenated product efuent to provide a hydrocarbon fraction having an initial boiling point of at least about 400 F.; reacting said hydrocarbon fraction with hydrogen at hydrocracking conditions, and in contact with a hydrocracking catalyst; commingling the resulting hydrocracked product effluent with said aromatic-containing charge stock and reacting the same with hydrogen as aforesaid.

Another broad embodiment of the present invention encompasses a process for converting an aromatic-containing hydrocarbonaceous charge stock to lower-boiling hydrocarbon products, which process comprises the steps of (a) commingling said charge stock with a previously hydrocracked product and hydrogen, reacting said charge stock in contact with a non-siliceous hydrogenation catalyst containing at least one metallic component selected from the platinum-group of the Periodic Table, at hydrogenation conditions including a temperature above about 300 F. selected to hydrogenate aromatic compounds and to provide a maximum hydrogenation catalyst temperature less than about 650 F.; (b) separating the resulting substantially aromatic-free hydrogenated product effluent to provide a hydrogen-rich gaseous phase and a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 F.; (c) commingling said gaseous phase and said hydrocarbon fraction and reacting the same in contact with an alumina-silica hydrocracking catalyst containing at least one metallic component selected from the metals and compounds of Group VIII of the Periodic Table, and at hydrocracking conditions including a temperature within the range of from about 200 F. to about 800 F.; (d) commingling the resulting hydrocracked product effluent with said aromaticcontaining charge stock and hydrogen, and hydrogenating the resulting mixture as aforesaid.

The applicability of the present invention for the production of the lower-boiling hydrocarbon products from heavier hydrocarbonaceous material, accompanied by increased catalyst stability, may be more clearly understood by defining several of the terms and phrases employed within the specification and the appended claims.

In those instances where temperatures are given with respect to initial boiling points, boiling ranges, and end boiling points, it is understood that the temperatures have reference to those which are obtained through the use of standard ASTM distillation methods. The term hydrocarbons, or hydrocarbonaceous material, connotes saturated hydrocarbons, straight-chain and branch-chain hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons, naphthenic hydrocarbons, as well as various mixtures of hydrocarbons including hydrocarbon fractions and/ or hydrocarbon distillates. The various phrases, hydrocarbons boiling within the gasoline boiling range, gasoline boiling range hydrocarbons, and middle-distillate boiling range, have hereinbefore been dened with respect to the present specification. However, at least two modifications of the foregoing broad embodiments of the present invention are directed to the processing of a hydrocarbonaceous charge stock having a particular boiling range. Therefore, the phrase substantially within the middle-distillate boiling range, connotes a charge stock having an initial boiling point above about 400 F. to about 425 F., and of which at least about 80.0% by volume is distillable below a temperature of about 650 F. When converting an aromatic-containing charge stock of this particular boiling range, the present invention involves a process which comprises the steps of: (a) commingling said charge stock with a previously hydrocracked product and hydrogen, reacting said charge stock in contact With a non-siliceous, non-acidic hydrogenation catalyst containing at least one metallic component from the platinum-group of the Periodic Table, and at hydrogenation conditions including a temperature above about 300 F., selected to hydrogenate aromatic compounds and to provide a maximum hydrogenation catalyst temperature less than about 650 F.; (b) separating the resulting aromatic-free hydrogenated product effluent to provide a hydrogen-rich gaseous phase and a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 F.; (c) commingling said gaseous phase and said hydrocarbon fraction and reacting the same in contact with an alumina-silica hydrocracking catalyst containing from about 1.0% to about 10.0% by Weight of an iron-group metallic component, and at hydrocracking conditions including a temperature within the range of from about 200 F. to about 600 F.; (d) commingling the resulting hydrocracked product effluent with said aromatic-containing charge stock and hydrogen, and hydrogenating the resulting mixture as aforesaid.

Similarly, the phrase substantially above the middledistillate boiling range, connotes a hydrocarbon charge stock of which not more than about 20.0% by volume is distillable below a temperature of about 650 F. The modification of the present invention employed for converting an aromatic-containing charge stock of this boiling range comprises the steps of: (a) commingling said charge stock with a previously hydrocracked product and hydrogen, reacting said charge stock in contact with a non-siliceous, halogen-containing hydrogenation catalyst containing at least one metallic component from the platinum-group of the Periodic Table, and at hydrogenation conditions including a temperature above about 300 F. selected to hydrogenate aromatic compounds and to provide a maximum hydrogenation catalyst temperature less than about 650 F.; (b) separating the resulting aromatic-free hydrogenated product eluent to provide a hydrogen-rich gaseous phase and a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 F.; (c) commingling said gaseous phase and said hydrocarbon fraction and reacting the same in contact with an alumina-silica hydrocracking catalyst containing from about 1.0% to about 10.0% by Weight of an iron-group metallic component, and at hydrocracking conditions including a temperature within the range of from about 400 F. to about 800 F.; (d) commingling the resulting hydrocracked product effluent with said aromatic-containing charge stock and hydrogen, and hydrogenating the resulting mixture as aforesaid.

From the foregoing embodiments, it will be noted that the process of the present invention utilizes at least two reaction zones, one of which serves to hydrogenate aromatic compounds, the other to convert a substantially aromatic-free charge stock into lower-boiling hydrocarbon products. A preferred mode of operation involves a particular arrangement of these reaction zones in a single reaction chamber, and comprises the steps of: (a) passing a mixture of said aromatic-containing charge stock and hydrogen into a reaction chamber containing an upper zone of an acidic hydrocracking catalyst and a separated lower zone of an non-siliceous hydrogenation catalyst, said mixture being introduced at a point intermediate said upper and lower zones, and admixed therein with a previously hydrocracked product from said upper zone; (b) reacting said charge stock and hydrogen at hydrogenation conditions selected to hydrogenate aromatic compounds without substantial conversion of said charge stock into lower-boiling hydrocarbons; (c) separating the resulting hydrogenated, substantially aromatic-free product eiiiuent to provide a hydrocarbon fraction having an initial boiling point of at least about 400 F.; (d) reacting said hydrocarbon fraction and hydrogen in contact With said upper zone of hydrocracking catalyst and at hydrocracking conditions including a temperature above about 200 F., commingling the resulting hydrocracked product effluent with said aromatic-containing charge stock and hydrogen, and reacting the same as aforesaid.

With respect to the various catalytic composites employed within the reaction zones of the process of the present invention, the term metallic component, or catalytically active metallic component, is intended to encompass those components of the catalyst which are employed for their hydrorefining, hydrogenation and/or hydrocracking activity. ln this manner, the catalytically active metallic components are distinguished from those components which are employed as the carrier material, or the acidic cracking component, or both. As hereinafter set forth in greater detail ,the process of the present invention utilizes particular catalytic composites in combination with particular operating conditions.

The present invention involves a process which is generally applicable to processing petroleum-derived feed stocks of the middle-distillate boiling range and above. Suitable charge stocks include relatively high-boiling hydrocarbon distillate fractions such as gas oil fractions, lubricating and White oil stocks; cycle stocks, slurry oils, black oil stocks, the various high-boiling bottoms recovered from the fractionators integrated within catalytic cracking operations, and referred to as heavy recycle stocks; fuel oil stocks, crude petroleum oils, reduced and/or topped crude oils, and other sources of hydrocarbons having a depreciated market demand due to a relatively high boiling point and to the presence of various contaminating influences including nitrogenous and sulfurous compounds, and asphaltic and other heavy hydrocarbonaceous residues. Accordingly, the hydrocarbon charge stock may consist entirely of a heavy vacuum gas oil or recycle stock, boiling Within the range of from about 650 F. to about 1100" F., or more. The l'iydrocarbonaceous material may be a light cycle oil bollig entirely within the middle-distillate or fuel oil boiling range, or it may be a vacuum gas oil having the boiling range of from about 600 F. to about 950 F. lt is understood, therefore, that the process of the present invention is not strictly limited to the use of a particular hydrocarbon mixture as the charge stock, although the same is especially adaptable for processing hydrocarbons which boil substantially completely at temperatures above the middle-distillate boiling range.

All of the foregoing heavy hydrocarbonaceous fractions and/or distillates generally contain high-boiling nitrogenous compounds, in adidtion to substantial quantities of sulfurous compounds, as contaminants. The presence of such nitrogen-containing compounds not only suppresses the hydrocracking activity of the catalytic composite, but also promotes the relatively rapid deactivation of the catalytically active metallic components, thereby resulting in catalyst instability. Nitrogenous compounds exhibiting this detrimental effect include both organic and inorganic nitrogen-containing compounds, aliphatic and aryl amines, ammonium compounds, heterocyclic organic nitrogen compounds such as pyridine, carbazole, pyrrole, and various derivatives thereof, quinoline, etc. As hereinbefore set forth, the deactivation of the catalytic composites appears to be due to the reaction of the nitrogen-containing compound with the various catalytic components, the extent of such deactivation increasing as the process continues. Although neutralization appears to be a factor which contributes to the catalyst deactivation, it is believed that the formation of a nitrogen-containing complex with the various catalytic components, whereby the active centers of the catalyst, normally available to the hydrocarbon charge stock, are effectively shielded therefrom, is the more predominating effect having the greatest influence in regard to catalyst deactivation. That is to say, the deactivating influence exhibited by nitrogenous compounds appears to be signicantly greater than that exhibited by sulfurous compounds, although both exist within the hydrocarbon charge stock in excessive quantities. Furthermore, the higher the concentration of nitrogenous compounds, or hydrocracking Suppressors, the higher the temperature required to elfect a given degree of conversion to lowerboiling hydrocarbon products, all other conditions being relatively equal. As the operating temperature is increased, the tendency to produce greater quantities of gaseous, light paraiiinic hydrocarbons becomes more pronounced. Another feature attendant the higher nitrogen content is that more frequent shut downs for the purpose of catalyst regeneration and/ or replacement are required. Increasing the temperature, to maintain a constant, acceptable conversion to lower-boiling hydrocarbon products, results in such product quality and distribution that it becomes necessary to regenerate the catalyst, the principal factor determining the stage of the process at which regeneration must be effected, being the excessive quantity of dry gas produced.

It has been recognized that the presence of excessive quantities of nitrogenous compounds, even as low as about 10 p.p.m., calculated as elemental nitrogen, will effectively poison acidic hydrocracking catalysts, and further, that the deleterious effect of the nitrogenous compounds is of a greater degree than that exhibited by the inclusion of sulfurous compounds. Provisions are necessarily made, therefore, to eliminate and/or decrease the concentration of the nitrogenous and sulfurous compounds prior to processing the hydrocarbonaceous charge stock in contact with the hydrocracking catalyst. Particularly preferred means for decreasing the quantity of nitrogenous compounds involves pretreating the hydrocarbonaceous material in a hydrorening process, in which process the material is subjected to catalytic action at reaction conditions such that the structure of the hydrocarbon components is not substantially altered, but the nitrogenous, organically-bound components are converted into ammonia and a corresponding hydocarbon. Although a hydrorefining pretreatment process is generally preferred, other pretreating methods may be suitably employed. For example, the hydrocarbonaceous material may be intimately contacted with various acidic media such as hydrofluoric acid, fuming sulfuric acid, etc., and, in those instances where the concentration of nitrogenous compounds is not excessive, acidic ion-exchange resins may be employed. It is understood that the particular means selected for eliminating the contaminating inuence of nitrogenous and sulfurous compounds is not essential to the present invention, although the utilization of a hydroreiining reaction zone is preferred from the standpoint of effecting nitrogen removal to a level less than about 10 p.p.m., and preferably less than about 2 p.p.m. Nothwithstanding that the hydrocarbonaceous material is subjected to a pretreating process for the purpose of decreasing the concentration of nitrogenous and sulfurous compounds, it has been found that a contaminating inuence in the form of aromatic compounds remains within the hydrocarbon charge stock. In addition to high-boiling, alkyl-substituted mononuclear aromatics, such aromatic compounds include naphthalene and its various derivatives such as naphthonic acid, naphthoquinone, etc.; anthracene, pyrene, triphenylene, chrysene, perylene, naphthacene and a Wide variety of alkyl-substituted aromatic compounds. At least a portion of the foregoing aromatic compounds appear to be unaffected by the pretreating process selected to eliminate the contaminating influence of the nitrogenous compounds, and remain in the hydrocarbonaceous material. The deleterious effects of the presence of aromatic compounds within the pretreated charge to the hydrocracking process, are primarily two-fold: (l) certain condensed aromatics appear to be adsorbed on. the acidic surface without being either hydrogenated, or cracked, and the catalytic surfaces and centers are therefore actively shielded from the material being processed; (2) the hydrogenation of the aromatic compounds is exothermic and promotes a premature degree of hydrocracking, raising the temperature to a still higher level and causing a temperature run-away. The net result of the temperature run-away is the unabated conversion of normally liquid hydrocarbons into excessively large amounts of light parainic hydrocarbons, accompanied by the virtually immediate deposition of large quantities of coke and other hydrocarbonaceous material onto the catalytic composite. These detrimental results are not simply eliminated and/ or controlled by decreasing the operating temperatures; a certain temperature level is required to trigger the hydrocracking reactions and, at this minimum level, the temperature increase resulting from the hydrogenation and/or hydrocracking of the aromatic compound is already excessive.

The utilization of the process of the present invention affords an effective method by which the adverse effects otherwise resulting from the presence of the aromatic compounds within the hydrocracking charge stock are eliminated. Briefly, this is accomplished by processing the substantially nitrogen-free (containing less than about 2.0 p.p.m.), aromatic-containing charge stock over two separate and distinct catalysts; a hydrogenation catalyst Which does not promote hydrocracking to a great extent, but which is specifically tailored to effect the hydrogenation of the aromatic compounds, followed by an acidic hydrocracking catalyst which effects the conversion of the hydrocarbonaceous material into lowerboiling hydrocarbon products. The present invention may be more clearly understood through reference to the accompanying drawing which illustrates one particular embodiment thereof. It is not intended, however, that the process of the present invention be unduly limited to the embodiment so illustrated. In the drawing, various ow valves, control valves, coolers, condensers, overhead reflux condensers, pumps, compressors, etc., have either been eliminated, or greatly reduced in number as not being essential to the complete understanding of the present process. The utilization of such miscellaneous appurtenances will immediately be recognized by onepossessing the requisite skill within the art of petroleum processing techniques. With reference now to the drawing, the hydrocarbonaceous material, contaminated by a substantial quantity of nitrogenous compounds of the order of about 1000 p.p.m. to about 8000 p.p.m. and sulfurous compounds in an amount of about 2.0% to about 8.0% by Weight, enters the process through line 1, is admixed with make-up hydrogen from line 2, the mixture continuing through line 1 into heater 3. The mixture of hydrogen and hydrocarbonaceous material entering heater 3 is such that hydrogen is present in an amount within the range of about 1000 to about 10,000 standard cubic feet per barrel, and preferably from about 3000 to about 8000 standard cubic feet per barrel. The function served by heater 3 is to raise the temperature of the hydrogenhydrocarbon mixture to the level desired at the inlet of the catalyst bed disposed Within hydroretining zone 5. The temperature of the mixture leaving heater 3 through line 4, and entering hydrorelining zone 5 will be within the range of about 500 F. to about 800 F., the maximum catalyst temperature within hydrorening zone 5 preferably being maintained Within the range of about 600 F. to an upper limit of about 850 F. The pressure within hydrorening zone 5 will be maintained Within the range of about to about 3000 pounds per square inch gauge, and preferably at an intermediate level of about 1000 to about 2000 pounds per square inch gauge; the liquid hourly space velocity (defined as volumes of liquid hydrocarbon charge per hour, per volume of catalyst disposed within the reaction zone) will be Within lthe range of about 0.25 to about 10.0, and preferably from about 0.5 to about 5.0. The precise operating conditions Will be dependent to a great extent upon the necessary degree of the removal of nitrogenous and sulfurous compounds, in addition to the hydrogenation of oleinic hydrocarbons contained within the hydrocarbonaceous charge stock. The catalytic composite disposed within hydrorefining zone 5, hereinafter described in greater detail, appears to function more efficiently and for an extended period of time when the maximum temperature therein during processing is less than about 850 F. Since the reactions occurring during the hydrorefining of the contaminated hydrocarbonaceous charge stock are somewhat exothermic, a rise in temperature will be experienced, and, therefore, the inlet temperature to the hydrorening catalyst bed is preferably maintained within the range of about 500 F. to about 800 F.

The total reaction product effluent from hydrorefining zone 5 is passed through line 6 into separator 7 which operates at essentially the same pressure existing in hydrorefining zone 5, but at a lower temperature of about 60 F. to about F. Separator 7 serves the function of providing a substantially nitrogen-free liquid hydrocarbon phase and an ammonia-containing gaseous phase. These are illustrated in the drawing as leaving separator 7 via lines 9 and 8 respectively. The gaseous phase in line 8 will contain hydrogen sulfide, hydrogen, ammonia and any light paraffinic hydrocarbons, methane, ethane and propane, resulting from the minor degree of cracking which occurs at the elevated temperatures necessary to effect acceptable removal of nitrogen and sulfur. This gaseous phase may be treated by ion-exchange, adsorption techniques, etc. for the purpose of recovering a substantially pure hydrogen stream, the latter being recycled by compressive means not illustrated in the drawing. ln any event, the normally liquid hydrocarbon portion of the hydrorelining zone effluent, leaving separator '7 through line 9, is substantially nitrogen-free, containing less than about 10 p.p.m. of nitrogenous compounds, calculated as elemental nitrogen, and preferably less than about 2.0 p.p.m. However, as hereinbefore stated, this normally liquid hydrocarbon fraction contains a significant quantity of monoand polynuclear aromatics which must necessarily be eliminated and/or greatly reduced in concentration in order to carry out an efficient, acceptable hydrocracking process.

After being admixed with additional hydrogen from line 10, the normally liquid hydrocarbons in line 9 are passed into heater 11 wherein the temperature thereof is raised to a level above about 300 F. The hydrogenhydrocarbon mixture in line 9 is such that the hydrogen is present in a mol ratio, to aromatic nuclei, greater than about 4:1. The precise temperature to which the mixture of hydrogen and aromatic-containing hydrocarbons is heated, is such that the maximum catalyst temperature existing in hydrogenation zone 14 is less than about 650 F.; thus, depending upon the precise quantity of aromatic hydrocarbons, the temperature, to which the mixture in line 9 is heated, will be within the range of about 300 F. to about 600 F. The mixture passes through line 12 into hydrogenation zone 1d, the latter being maintained at a pressure of from about 300 to about 3000 pounds per square incn gauge, and preferably at an intermediate level Within the range of about 1000 to about 2000 pounds per square inch gauge. It is noted that the hydrogen-hydrocarbon mixture in line 12 enters the reaction chamber at a point intermediate upper hydrocracking zone i3 and lower hydrogenation zone 14; upon entering the reaction chamber, the mixture is immediately commingled with the hydrocracked product eluent from upper hydrocracking zone i3. In this manner, the liquid hourly space velocity through hydrogenation zone i4 is increased due to the additional hydrocarbonaceous material from upper hydrocraciring zone 13; thus, the liquid hourly space velocity through hydrogenation zone i4 will be Within the range of about 1.0 to about 15.0. However, since the primary function of hydrogenation zone i4 is to hydrogenate the monoand polynuclear aromatics, without effecting a substantial degree of hydrocracling, the upper limits of the liquid hourly space velocity may be utilized as a means of controlling the degree of hydrocracking being effected. Controlling the degree of hydrocraclcing which is effected in hydrogenation zone i4 is one of the many advantages attendant the particular reaction chamber arrangement indicated in the drawing, in which arrangement the hydrocracking Zone is situated above the hydrogenation Zone: additional advantages of this arrangement are hereinafter described.

The catalyst disposed within hydrogenation zone 1d comprises at least one metallic component selected from the group consisting ot the metals of the platinum-group oi' the Periodic rlable, composited with a non-siliceous carrier material. The precise composition of the hydrogenation catalyst is partially dependent upon the boiling range of the hydrocarbonaceous charge stock entering through line l2. ln those instances Where the charge stock boils substantially within the middle-distillate boiling range, that is, at least about 80.0% by volume is distillable below a temperature of about 650 F., the hydrogenation catalyst will comprise a platinum-group metallic component, a non-siliceous, non-acidic carrier material and at least one metallic component selected from the group consisting of alkali and alkaline-earth metals. The preferred carrier material, for use with this hydrogenation catalyst, is alumina, the catalytically active metallic components being from about 0.01% to about 5.0% by weight of a platinum-group metal and from about 0.1% to about 2.0% by weight of at least one metal from the group of alkali .and alkaline-earth metals. The description oi the hydrogenation catalyst in this instance is hereinafter described in greater detail. When the hydrocarbonaceous charge stock inline l2 boils substantially at temperatures exceeding the middle-distillate range, that is, not more than about 20.0% by volume is distillable below a temperature of about 650 F., the catalyst disposed within hydrogenation zone ld will comprise a non-siliceous carrier material such as alumina, with which is composited from about 0.01% to about 5.0% by weight of a platinum-group metallic component and from about 0.1% to about 1.0% by weight oi halogen selected from the group consisting oi chlorine and iluorine. Contrary to what might be expected, the addition of a minor quantity of halogen Ato the hydrogenation catalyst, while processing a hydrocarbonaceous charge stock boiling substantially above the middle-distillate boiling range, and under the conditions imposed Within hydrogcnation Zone i4, does not impart unusual hydrocracking activity to the catalyst. The higher-boiling hydrocarbonaceous material will inherently contain higher-boiling polynuclear aromatic hydrocarbons which are somewhat more ditlicult to hydrogenate at a maximum catalyst temperature less than about 650 F., than are the lower-boiling polynuclear aromatic compounds. That is to say, the addition of from about 0.1% to about 1.0% by weight or" halogen to the alumina-platinum group metal catalyst, appears to facilitate the hydrogenation of the aromatic nuclei without promoting the hydrocracking of the normally liquid hydrocarbons which have not as yet passed through hydrocracking zone .13.

The primary function ot the catalyst within hydrogenation Zone 14 is to effect the saturation of the aromatic compounds remaining in the pretreated hydrocarbonaceous material following the processing through hydroretining zone 5. A relatively insignicant quantity of light paraiiinic hydrocarbons may be produced within hydrogenation zone 14 as a result of the dealkylation of at least a portion of the alkyl-substituted aromatic compounds. The total reaction chamber .effluent from hydrogenation zone 1.4 passes through line 15 into separator i6 from which a normally liquid hydrocarbon portion is withdrawn via line 20. A gaseous phase containing the relatively minor quantity of light paraiinic hydro carbons is withdrawn from separator i6 via line 17, and is recycled via line 27 to enter the reaction chamber at the upper portion of hydrocracking zone 13. In order to maintain control of the operating pressure imposed upon the reaction chamber, at least a portion of the gaseous phase in line 17 is withdrawn from the system through line i8 containing pressure control valve l?. Withdrawal of this gaseous phase from the system also prevents a continuing build-up of the light parainic hydrocarbons which would adversely affect the concentration of hydroge in hydrocracking zone 13 and hydrogenation zone ld, and would also adversely affect the space velocity therethrough.

The normally liquid product eilluent from the reaction chamber passes through line 20 into fractionator 21 at a point just above center well 22. Fractionator 2l is operated in such a manner as to provide the desired break down of the total reaction chamber etlluent. For example, as indicated in the drawing, light hydrocarbons such as butanes and pentanes may be removed from the uppermost extremity of fractionator 21 through line 26. From a point just above center Well 25, the remaining gasoline boiling range hydrocarbons, having an end boiling point of about 400 F. to about 425 F. are removed via line 24; in those instances Where economic considerations dictate the production of a nitrogen-free middle-distillate boiling range hydrocarbon fraction, boiling from about 400 F. or 425 F. to about 650 F., the same are withdrawn through line 23. That portion of the reaction chamber product eiliuent boiling above the middledistillate boiling range, or at a temperature above about 650 F., or, where maximum production of gasoline boiling range hydrocarbons is desired, boiling above a te.. perature of about 425 F., are removed from fractionator 21 via line 27 and are passed therethrough into the upper portion of the reaction chamber containing hydrocracking zone It. Prior to entering hydrocracking zone 13, the hydrocarbonaceous material in line 27 is admixed with the hydrogen-rich gaseous phase in line 17 from separator 16. The amount of hydrogen entering hydrocraclring Zone 13, in admixture with the liquid hydrocarbons in line 27, is within the range of about 1000 to about 10,000 standard cubic feet per barrel, and preferably from about 3000 to about 8000 standard cubic feet per barrel. It is readily ascertained, therefore, that .the quantity of hydrogen in admixture with the hydrorerined product eiuent in line 12, entering the reaction chamber at a point intermediate hydrocracking Zone 13 and hydrogcnation zone if, must necessarily be sufcient to hydrogenate the aromatic compounds and to supply that In many instances wherein a particular degree of hydrocracking activity is desirable, the hydrorelining catalyst may contain from about 0.2% to about 10.0% by weight of an iron-group metallic component. Thus, the catalyst utilized in the hydrorcfining reaction zone may comprise from about 10.0% to about 25.0% by weight of molybdenum, from about 1.0% to about 6.0% by weight of nickel composited with alumina; 6.0% by weight of molybdenum, 1.5% by weight of nickel and 0.25% by weight of cobalt composited with an aluminasilica carrier ma terial in which the silica is present in an amount of about 1.0% to about 12.0%; 1.1% by weight of cobalt, 5.6% by weight of molybdenum on a carrier material consisting essentially of 100% by weight of alumina, etc.

The catalytic composite utilized in the hydrorefining reaction zone may be manufactured in any suitable manner, and it is understood that the precise method is not considered as a limiting feature of the present invention. Particularly advantageous methods utilize impregnating techniques; thus, where the catalyst is to contain both nickel and molybdenum, for example, the method of preparation involves forming aqueous solutions of watersoluble compounds such as nickel nitrate, nickel carbonate, ammonium molybdate, molybdic acid, etc. The preformed refractory inorganic oxide particles, serving as the carrier material, are commingling with the aforementioned aqueous solutions and subsequently dried at a temperature of about 200', F., the dried composite being oxidized in an oxidizing atmosphere at an elevated temperature of from about 1100' F. to about 1700 F. The impregnating technique may be effected in any manner; the carrier material may be impregnated first with the molybdenum-containing solution, dried and oxidized. and subsequently impregnated with the nickel-containing solution. On the other hand, the two aqueous solutions may be first intimately commingled with cach other, the carrier material subsequently impregnated -in a single step. The final catalytic composite may be treated to convert the metallic components into a particularly desired form. Thus, although the quantities of the mctallic components are computed on the basis of the elcmental metals, the same may exist as the elemental metal, or as the oxides, sulfides, etc.

A feature of the present invention resides in the particular catalytic composite employed in the lower hydrogcnation zone of the reaction chamber. In order to avoid excessive hydrocracking reactions in the presence of the monoand particularly polynuclear aromatic compounds, the catalytic composite is characterized as being non-siliceous. In those instances where the charge stock boils substantially within the middle-distillate boilingl range, hereinbefore defined as 80.0 volume percent distillable below a temperature of about 650 F., the catalyst is also characterized by being nonacidic. However, in those instances where the charge stock boils substantially above the middle-distillate boiling range, the catalytic composite may contain up to about 1.0% by weight of an acidic component, such as halogen from the group of chlorine and/or fiuorine. In any event, the catalytically active metallic components areeomposited with a non-siliceous refractory inorganic oxide which does not` contain excessive quantities of acidic-acting components. As hereinbefore stated, the utilization of from about 0.1% to about 1.0% by weight of halogen, when processing the heavier hydrocarbonaeeous material, facilitates the hydrogenation of the higher-boiling polynuclear aromatic compounds without promoting the undesirable ex cessive hydrocracklng reaction in the presence of these aromatic compounds. When the catalytic composite is desired to be both non-siliceous and non-acidic, such acidic-acting components as silica and the'components from the halogen family are excluded, and the catalyst comprises a carrier'material which ls preferably composited with a platinum group metal component and an alkali metal and/or alkalineearth metal component. It

is understood that the platinum-groupmetal and/or other metallic component may be present either as the element, or as a chemical compound, or in physical association with the other catalytic components; in any event, the concentrations are computed on the basis of the elemental metal. The platinum-group metallic component may bc platinum, palladium, ruthenium, rhodium, iridium, osmum, although platinum and/or palladium appear to yield more advantageous results. In general, 'the platinum-group component will be utilized in a concentration of from about 0.01% to about 5.0% by weight of the final catalyst, although suitable catalysts may be manufactured to contain intermediate quantities within the rango of about 0.1% to about 2.0% by weight. The alkali metal and/or alkaline-earth metal component, such as cesium, lithium, rubidium, sodium, calcium, magnesium, and/or strontium, will be employed in a concentration of not more than about 5.0% by weight of the catalyst; in order to achieve a proper balance between inhibiting the occurrence of side reactions, and imparting the desired degree of stability to the platinum-group metal-containing catalyst with respect to the hydrogenation of the aromatic compounds, it is preferred to employ the alkali and/or alkalineearth metals in significantly lower concentrations. Therefore, they will be present in a concentration within the range of from about 0.01% to about 0.7% by weight, calculated as the element thereof.

The hydrogenation catalyst may be prepared in any suitable manner, and it is understood that the particular method of manufacture is neither essential to, nor limiting upon the present invention. In general, alumina may be prepared by reacting a suitable alkaline reagent including ammonium hydroxide, ammonium carbonate, etc., with a salt of aluminum including aluminum chloride, aluminum sulfide, aluminum nitrate, etc. the substances are intimately admixed under conditions to form aluminum hydroxide which, upon subsequent heating and drying, will form alumina. The platinum-group metallic component, and the alkali metal or the alkaline-earth metal component, are added by way of impregnating techniques utilizing aqueous solutions of'these metals. It is generally advisable to introduce the platinum-group metallic component at a later step of the catalyst preparation in order that this relatively expensive metallic component will not be lost in subsequent processing. The catalyst is generally dried at a temperature of about 200 F., followed by a calcination treatment at a temperature of from about 800' F. to about 1100 F. for a period of frfom about 2 to about 12 hours, and in an atmosphere o air.

Catalytic composites which comprise at least one metallic component selected from Groups VI-A and V111 of the Periodic Table, and a composite of silica and from about 10.0% to about 90.0% by weight of alumina, constitute hydroeracking catalysts for use in the hydrocrack- .ing reaction zone of the process of the present invention.

Such catalysts have a relatively high activity with respect to the conversion of hydrocarbons boiling within and above the middlefdistillate boiling range, into hydrocarbon products boiling within the gasoline boiling range. Furthermore, in those instances where the hydrocarbonaccous f charge stock boils almost entirely at a temperature ex ceeding the middle-distillate boiling range (650 F.), such catalysts readily adapt themselves for utilization in producing both middle-distillate boiling range hydrocarbons and gasoline boiling range hydrocarbons.

The synthetically-produced, acid-acting carrier material, for utilization in the upper hydrocracking zone of the reaction chamber, may be made in any suitable manner including separate, successive, or coprccipitation methods. For example, in the separate precipitation method, the refractory oxides are precipitated separately and then mixed in the wet state; when successive precipitation methods are employed, the first oxide is precipitated, and the wet slurry thereof, either with or without acidulated water or other means to remove sodium ions,l

subsequently commingly with an aluminum salt such as aluminum chloride, and/or some suitable zirconium salt, and either adding a basic precipitant such as ammonium hydroxide, or forming the desired oxide or oxides through,

the thermal decomposition of the salt, as the case may be. As with the catalytic composites disposed within the hydrorcning reaction zone and the lower hydrogenationV zone of the reaction chamber, the particular means utilizcd for the manufacture of the catalyst disposed within the upper hydrocracking zone is not considered to be la limiting feature of the process of the present invention.

The catalytically active metallic components are generally employed in an amount of from about 0.1% to about 20.0% by weight of the total catalyst, and are computed on the basis of the elemental metals. The hydrocracking catalyst comprises at least one metallic component selected from the metals of Groups VI-A and Vlll of the Periodic Table,nnd includes, therefore, platinum, palladium, nickel, iron, cobalt, molybdenum, tung sten, chromium, ruthenium, rhodium, iridium, etc., and these may be incorporated with the acidic-acting carrier material in any suitable manner. When silica and alumina are employed as the carrier material in combination, the latter will be present within an amount of from about 10.0% to about 90.0% by weight. Excellent results have been achieved through the utilization of the following silica-alumina composites; 88% by weight of silica and 12% by weight of alumina, 75% by weight of silica and by weight of alumina, 63% by weight of silica and 37% by weight of alumina, and 88% by weight of alumina and 12% by weight of silica. The Group VI-A metal,

cracking catalyst, whereby the processing of the higherboiling charge stocks may be accomplished at comparatively lower operating temperatures. Such halogen is generally selected from the group of chlorine and/or tiuorine, and will be present within the composite in an amount of from about 1.0% to about 8.0% by weight, calculated as the element although referred to as combined halogen. The halogen may be composited with the catalyst in any suitable manner including theutilization of a volatile salt such as ammonium chloride and ammonium fluoride, or acids such as hydrochloric acid and hydrofluoric acid, or during the manufacture of the carrier material as when aluminum chloride `is employed as the source of aluminum. It is understood that the broad scope of the present invention is not to be unduly limited to the utilization of a particular catalyst having a particular concentration of components, a particular means for the manufacture of the same, or specific operating conditions other than those previously set forth. The utilization of any of the previously mentioned catalytic composites, at operating conditions varying within the limits hereinbefore set forth does not necessarily yield results equivalent to the utilization of other catalytic composites employed under other operating conditions. The precise nature of the catalyst' employed and the exact operatingl conditions in the various reaction zones, are at least partially dependent upon thc physical and/or chemical characteristics of the highboiling hydrocarbon fraction being subjected thereto. Furthennore, the operating conditions will be dependent upon the quality and quantity of the normally liquid hydrocarbon product desired as the end result. Through the utilization of the process of the present invention,

such as chromium, molybdenum, or tungsten, when utilized within the hydrocracking catalyst, is usually present in quantities within the range of from about 0.5% to about 20.0% by weight of the final catalyst. The Group VIII metals, which may be divided into two'subgroups, are present in an amount of from about 0.1% to about 10.0% by weight of the final catalyst. When an iron subgroup metal such as iron, cobalt, or nickel, is employed, it is present in an amount of from about 0.2% to about 10.0% by weight, and preferably from about 1.0% to about 6.0%, whereas the platinum-group metals such as platinum, palladium, iridium, rhodium, etc., is present in an amount within the range of from about 0.1% to about 5.0% by weight of the total catalyst. When the metallic component of the hydrocracking catalyst consists of both a Group VI-A and a Group VIII metal, lt will contain metals of this group in a ratio of from about 0.0521 to about 5.0:1 of the Group Vlll metallic components to the Group Vl-A metallic components. Suitable catalytic composites, for utilization in the hydrocracking zone, comprise the following, but not by way of limitation: 6.0% by weight of nickel and 0.2% by weight of molybdenum; 1.8% by weight of nickel and 16.0% by weight of molybdenum; 6.0% by weight nickel; 0.4% by weight of palladium; 6.0% by Weight of nickel and 0.2% by weight of platinum; 6.0% by weight of nickel and 0.2% by weight of iron; 0.4% by weight of platinum; 6.0% by weight of nickel and 12.0% by weight of molybdenum, etc.

In many instances, particularly when the catalytically active metallic components comprise metals selected from the platinum-group of Group VIII of the Periodic Table, it will be desirable to in'clude a halogen component to imgreater concentrations of hydrocarbons boiling within the normal gasoline and middle-distillate boiling ranges are produced. It is possible to effect such conversions over an extended period of time due tothe greater degree of stability imparted to the various catalytic composites, and particularly to the hydrocracking catalyst as a result of the particular. decontamination of the charge stock as hereinbefore described. A degree of flexibility within the process is aiforded,'with the result that greater concentrations of gasoline boiling range hydrocarbons may be subsequently produced from the middle-distillate boiling range hydrocarbons contained within the product etiluent, by recycling the latter to combine with the hydrocarbon charge stock. The overall picture indicates extended catalyst stability over a prolonged period of time in addition to a substantial reduction in the quantity of light paraftinic hydrocarbons otherwise resulting from the nonselective, uncontrolled hydrocracking of hydrocarbons, and particularly when effected in the presence of polynuclear aromatic compounds which inherently result in relatively rapid catalyst deactivation. Although the method of the present invention, and the operating conditions utilized therein, are such that the etlective life of the catalytic composites are prolonged over an extended period of time, catalyst regeneration may eventually become desired due to the natural deterioration of the catalytically active metallic components thereof. In general, the catalytic composites may be readily regenerated by contacting the deactivated catalyst with a free oxygen- Y containing gaseous material, such as air, at temperatures within the range of from about 700' F. to about 1400 F., for the purpose of removing coke and other heavy hydrocarbonaceous material therefrom. The resulting metal oxide may then be converted to a substantially reduced state through the utilization of a reducing atmosphere such as hydrogen, and, with respect to those catalytic eompositcs utilizing combined halogen, the halogen may be replaced, where necessary, through the utilization of hydrogen halide, ahalogen-containing gaseous phase, ete.

With respect to the conversion of the hydrocarbonapart an additional acidic-acting function to the hydro- @cous charge stock into lower-boiling hydrocarbon products, high conversions of the charge material into gasoline boiling range hydrocarbons are generally effected at temperatures within the range of from about 200 F. to about 800 F. In many instances, depending upon the character of the charge stock and the desired end results, the hydrocracking reaction zone will operate at a catalyst temperature within the range of about 200'( F. to about 600 F., as where the charge stock thereto boils substantially within the middle-distillate boiling range. On the other hand, temperatures within the range of from about 400 F. to about 800 F. will generally be utilized when processing hydrocarbon charge stocks boiling substantially completely above a temperature of about 650 F. In addition, the precise temperature will .depend upon, and may be correlated with the liquid hourly space velocity as well as the current instantaneous life of the catalyst. The precise operating temperature may be readily determined by those skilled in the art when considering the character and composition of the catalytic composite, the liquid hourly space velocity and/or `tho physical and chemical characteristics of the high-boiling hydrocarbon charge stock, as well as the desired end result. In any cvcnt, the quantity of light parat'nic hydrocarbons, methane, ethane, propane, at any particular conversion level is extremely low. The present process achieves etlicicnt conversion with minimum losses from deposition of coke and carbonaceous material, and the production of undesirable light paraflinic hydrocarbons. Although the temperature and liquid hourly space velocity are the main factors affecting the degree of conversion into hydrocarbon products boiling within the normal and middledistillate boiling ranges, at a given temperature level the liquid hourly space velocity docs not substantially affect the quantity of dry gas produced. The primary effect of varying the quantity of hydrogen through the hydrogenation and hydrocracking zones, and the hydrogen pressure imposed thereupon, is the effect upon the amount of coke and carbonaceous material produced. Notwithstanding lower pressures and/or lower hydrogen rates, both as hcreinbefore specified, there is very little coke formation otherwise experienced at the selective operating conditions when processing a hydrocarbonaceous material in which the polynuclear aromatica exist in a high concen tration. It will be recognized, therefore, that the variables must be primarily correlated to produce high yields of gasoline and middle-distillate hydrocarbons, and minor quantities of dry gas, and that such correlations may be readily made by one possessing skill in the art of petroleum processing.

The following examples are given to illustrate further the process of the present invention, and to indicate the bcnets to be afforded through the utilization thereof.

generally broad scope and spirit of the appended claims.

The hydrocarbonaceous charge stock utilized to illustrate the benefits afforded as a result of the prehydrogenation of the polynuclear aromatic hydrocarbons, prior to subjecting the hydrocarbonaceous material to the hydrocracking reaction zone, was a light cycle oil having the analysis indicated in the Afollowing Table I. It should be noted that the light cycle oil was severely contaminated by sulfurous compounds in an amount of 2.21% by weight, calculated as elemental sulfur, in addition to 126 p.p.m. of nitrogen. Therefore, the light cycle oil could not immediately be subjected to hydrocracking without experiencing rapid catalyst deactivation and extremely low conversion into hydrocarbons boiling within the normal gasoline boiling range (having an end boiling point of about 400 F. to about 425 E). The light cycle oil, as received, was subjected to hydroretining for the purpose of effecting the destructive removal of the high boiling sulfurous and nitrogenous compounds.

1lir

i 1t is understood that the examples are given for thesol'c purpose of illustration. and are not considered to limit the The catalyst utilized in the hydroretinng process was a composite of 11.3% by weight of molybdenum, 4.2% by weight of nickel and 0.05% by weight of cobalt, all of which had been impregnated within a carrier material consisting of 88.0% by weight of alumina and 12.0% by weightof silica in the form of Mrinch spheres. Following the drying of the impregnated spherical particles, the composite was subjected to the high-temperature oxidation treatment hereinbefore described; in this particular instance it was desired that the catalytically active metallic components exist within the composite as the sulfides thereof; therefore, the oxidized composite was sulfded at a temperature of about 750 F. in an atmosphere containing hydrogen sulfide. The hydrorening conditions, under which the light cycle oil was processed, were a liquid hourly space velocity of 0.5, a pressure of 900 pounds per square inch gauge, and an inlet temperature to the catalyst bed of 658 F. (resulting in a maximum catalyst temperature of about 761 12.), and in the presence of 10,000 standard cubic feet of hydrogen per barrel of liquid hydrocarbon charge. It is recognized that these conditions are extremely severe, and, as indicated in Table I, etected a slight change in the boiling range and gravity of the light cycle oil. However, it was desired, for the purpose of illustrating the process of the present invention, to produce an ultra-clean hydrocarbon mixture to be subsequently subjected to hydrocracking. As further indicated in Table I, notwithstanding the severe hydrorening conditions, and the unusually large quantity of hydrogen present within the hydrorening reaction zone, the hydrorened liquid product contained polynuclear aromatics, calculated as anthracene, in an amount of p.p.m.

Example I and drying, the catalyst was calcined fora period of 3 hours at a temperature of 1300 F. in a vertical furnace tilizing dry nitrogen at a rate of about lo cubic foot per our.

The hydrocracking reaction zone was maintained under a hydrogen pressure of about 1500 pounds per square inch gauge', a temperature of about 600 F., having a liquid hourly space velocity of 2.0 through the catalyst. As indicated in the following Table II, after a catalyst life ot 16 hours at a hydrogen recycle rate ot 10,000 standard cubic feet per barrel ot hydrocarbon charge (period A), the normally liquid portion ot the product etiluent indicated a gravity, API at 60 F., of 60.0, and a conversion to hydrocarbons boiling below 400 F., of 84.0%

TABLE I`I.HYDROCRACKING WITHOUT PRH HYDROGENATION Period Designation O ating Conditions: porlempersture F Pressure .alg

Liquid rigori, s

Catal t Lite, ours Product n API g 00 F 6 400' alyssa: Li uid Gravity, Vo urne Percent Example II In this example, the hydrocraclting catalyst consisted of 0.4% by weight of palladium composited with the silica-alumina spheres described in conjunction with the foregoing Example I, containing, however, 1.9% by.

weight of combined uoride, calculated as elemental iluorine. The catalyst was prepared by impregnatng 468 grams of the silica-alumina carrier material witha solution of 26.2 grams of hydrouoric scid (48.0% by weight of hydrogen fluoride), diluted to 350 cc. and admixed with 57.5 cc. of a 28.0% by weight solution of ammonia. After impregnation and drying, the catalyst was oxidized for a period of l hour at a temperature of 1000 F. 130 grams of the tiuorided'aluminaailica particles were impregnated with 170 cc. of an aqueous solution containing 29 cc. of palladium chloride (0.018 gram of palladium per ec.). After impregnation and drying, the catalyst was calcined for a period of l hour at a temperature of 1300 F.

The processing of the hydroreiined light cycle oil was intentionally conducted at low-severity hydrocracking conditions. As indicated in the following Table III, for example, the liquid hourly space velocity was increased to 4.0, as compared to 2.0 in Example I, and the reactor maintained at a temperature of 473' F. (period C) and 491 F. (period D). As indicated by the analyses obtained on the normally liquid portion of the product eiiluent, the hydrocracking catalyst deactivated at a relatively rapid rate. The volume percent conversion to gasoline boiling range hydrocarbons decreased from 27.0 to 11.5, accompanied by a corresponding increase in the initial boiling point thereof from 175 F. to 205 F. Similarly, there was a decrease in the gravity, API at 60F., of from 42.6 to 36.3.

TABLE IIL-LOW-SBVERITY HYDROCRACKING lcriod Designation Operating Conditions:

Temperature C Pressure p.s. .g Liquid :lenny e vetoetty. llydrogen s.e.I.lbbl

Catal st Life, ours Product yses:

Gravity API G F Volume eroent 400* L.-. Initial Boiling Po t, l.

massaal Example III square inch space velocity of 6.0 and a pressure of 1500 pounds per gauge. The catalyst was a non-siliceous, halogen-free alumina carrier material containing 0.75% by weight of platinum and 0.274% by weight of lithium, calculated as the elements thereof. The incorporation of the platinum and lithium with the spherical alumina particles involved a simultaneous `impregnation technique with a single aqueous solution of lithium hydroxide and chloroplatinic acid. The impregnated spherical particles were dried over a water bath at about 210 F. and subsequently calcined for a period of 5 hours at a tempera-l ture of about 1800 F., and in an atmosphere of air. The analysis of the pre-hydrogenated, hydrorefined iight cycle oil is given in the following Table IV.l lt is noted that the polynuclear aromatic concentration has decreased from 75 p.p.m. to 2.8 p.p.m., and that there has been a decrease in the quantity of nitrogen from 0.27 p.p.m. to 0.14 p.p.m. The lowering of the initial boiling point, from a level of 400F. to 385 F., is attributed to the lower concentrations of polynuclear aromatica and nitrogen, and a slight degree of dealkylation of the alkyl-substituted hydrocarbons contained within the light cycle oil.

TABLE IV.PREHYDROGENATED HYDRO- REFINED LIGHT CYCLE OIL The pre-hydrogenated light cycle oil was processed over a hydrocracking catalyst containing 5.0%` by weight of nickel composited with linch by l-inch silica-alumina cylindrical pills, at a temperature oi 621 F., a pressure of about1500 pounds per square inch gauge and at a liquid hourly space velocity of about 2.0. For 300 hours of operation, the gravity, API at 60 F., of the normally liquid portion of the product eiiiuent was virtually constant at 48.0. During the period of operation covering approximately 300 hours to 312 hours, the prehydrogenated charge stock was removed and the hydroreiined (but not pre-hydrogenated) light cycle oil was utilized as the charge stock. During the on-stream time of 300 hours to 312 hours, while the change in charge stocks was being effected, the gravity ofthe normally liquid product eniuent decreased from 48.0 to 42.0. From 312 hours to 330 hours oI operation, the API gravity decreased from 42.0to 38.0 and indicated a continuing rapid decline. At 330 hours of operation, the operating temperature was increased to 658 F., and this was accompanied by a corresponding increase in gravity of the normaily liquid hydrocarbon product from 38.0 to 46.5. From about 340 hours to about 362 hours, maintaining the temperature at about 658 F., the gravity of the product eiuent was decreased from 46.5 to 41.5, and was indicating a relatively rapid decline.

A second operation was conducted wherein the hydroreiined light cycle oil was pre-hydrogenated, utilizing the previously described platinum-lithium catalyst, at a pressure o! 1500 pounds per square inch gauge and a liquid hourly space velocity of 4.0, accompanied by a hydrogen recycle rate ot 6000 standard cubic feet per barrel. The prehydrogenated product etiluent was subjected to hydrocracklng utilizing a catalyst of 5.0% by weight of nickel composited with an alumina-silica carrier material. The inlet temperature to the hydrocraclting catalyst bed was maintained at about 648 F., maintained at 1500 I pounds per square inch gauge, and at a hydrogen rate of 6000 standard cubic feet per barrel, with a liquid hourly s pace velocity of 4.0. Shortly after instituting this operation. the processing achieved unusual stability and remained so for a period of about 265 hours. In order to control the gravity of the normally liquid product effluent at about 50.0 API, at 60 F., the temperature of the hydrocracking catalyst was adjusted. The deactivation which was experienced, as indicated by the temperature adjustment of only 1.7 F. per barrel of charge, per pound of catalyst disposed within the hydrocraclting reaction zone, was that deactivation which is normally expected to result from the natural deterioration of the ycatalytcally active metallic components.

The foregoing Examples I and II indicate the detrimental results experienced when the hydrocracking charge stock contains polynuclear aromatica. Example III illustrates the benefits afforded through the utilization of the combined process of the present invention, in which the polynuclear aromatics are hydrogenated prior to effecting the hydrocracking reactions. Probably the most signiticant result is indicated by the definite increase in the stability of the hydrocracking catalyst to maintain a relatively constant, acceptable product quality over a prolonged period of time, without experiencing relatively rapid deactivation. Various modifications in the operating conditions and catalytic compositions may be made by one possessing skill within the art of petroleum processing, whereby the effective, acceptable life of the hydrocracking catalyst may be further extended. It is not intended that such modifications will remove the resulting plrocess from thebroad scope and spirit of the appended c aims.

I claim as my invention:

1. A process for converting a hydrocarbon charge stock containing aromatic compounds into lower-boiling hydrocarbon products which comprises commingling said charge stock with a previously hydrocracked product and hydrogen; reacting said charge stock and hydrogen at hydrogenation conditions and in contact with a nonsiliceous hydrogenation catalyst, said conditions and catalyst selected to hydrogenate aromatic compounds without substantial conversion of said charge stock into a lower-boiling hydrocarbon products; separation from the resulting substantially aromatic-free, hydrogenated product efiluent a hydrocarbon fraction having an initial boilin gpoint of at least about 400 F.; reacting said hydrocarbon fraction with hydrogen at hydrocracking conditions, and in contact with a hydrocracking catalyst; and commingling the total efiiuent from the hydrocraclting step with said aromatic-containing charge stock as said previously hydrocracked product.

2. A process for converting an aromatic-containing hydrocarbonaceous charge stock into lower-boiling hydrocarbon products which comprises the steps of:

(a) commingling said charge stock with a previously hydrocracked product, reacting said charge stock with hydrogen in contact with a non-siliceous hydrogenation catalyst, at hydrogenation conditions including a temperature above about 300 F. and selected to hydrogenate aromatic compoundsr without substantial conversion of said charge stock into lower-boiling hydrocarbons;

(b) separating from the resulting substantially aromatic-free, hydrogenated product etiluent a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 F.;

(c) reacting said hydrocarbon fraction with hydrogen at hydrocracking conditions including a temperature above about 200 F. and in contact with an acidic hydrocracking catalyst; and

(d) commingling the total efiluent from the hydrocracking step with said aromatic-containing charge stock as said previously hydrocracked product.

3. The process of claim 2 further characterized in that said hydrogenation catalyst comprises alumina and at least one metallic component selected from the group consisting of the metals of the platinum-group of the Periodic Table, and compounds thereof.

'4. -The process of claim 2 further characterized in that said hydrocracking catalyst comprises at least one metallic component selected from the group consisting of the metals and compounds of Group VIII of the Periodic Table, composited with an alumina-silica Vcarrier material.

5. A process for converting an aromatic-containing hydrocarbonaoeous charge stock into lower-boiling hydrocarbon products which comprises the steps of:

(a) commingling said charge stock with a previously hydrocracked product and hydrogen, reacting said charge stock in contact with a non-siliceous hydrogenation catalyst containing .at least one metallic component from the platinum-group of the Periodic Table, and at hydrogenation conditions including a temperature from about 350 F. to about 650 F. and a liquid hourly space velocity of from about 1.0 to about 15.0 correlated to hydrogenate aromatic compounds without effecting a substantial degree of hydrocracking;

(b) separating the resulting substantially aromaticfree hydrogenated product efuent to Aprovide a hydrogen-rich gaseous phase and a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 F.;

(c) commingling said gaseous phase and said hydrocarbon fraction and reacting the same in contact with an alumina-silica hydrocracking ca-talyst containing at least one metallic component from the metals and compounds of Group VIII of tbe Periodic Table, and at hydrocracking conditions including a temperature within the range of from about 200 F. to about 800 F.; and

- (d) commingling the total effluent from the hydrof cracking step with said aromatic-containing charge stock as said previously hydrocracked product.

6. The process of claim 5 further characterized in that said hydrocracking catalyst comprises from about 1.0% to about 10.0% by weight of an iron-group metallic component composited with an alumina-silica carrier material.

7. A process for converting an aromatic-containing hydrocarbonaceous charge stock boiling substantially within the middle-distillate boiling range, into lower-boiling hydrocarbon products which comprises the steps of:

(a) commingling said charge stock with a previously hydrocracked product and hydrogen, reacting said charge stock in contact with a non-siliceous, nonacidic hydrogenation catalyst containing at least one metallic component from the platinum-group of the Periodic Table, and at hydrogenation conditions including a temperature fromabout 350 F. to about 650 F. and a liquid hourly space velocity of from about 1.0 to about 15.0 correlated to hydrogenate aromatic compounds without effecting a substantial degree of hydrocraclting;

(b) separating the resulting aromatic-free hydrogenated product efuent to provide a hydrogen-rich gaseous phase and a normally liquid hydrocarbon fraction having an initial boiling point of at least about 400 (c) commingling said gaseous phase and said hydrocarbon fractonand reacting the same in contact with an alumina-silica hydrocraclting catalyst containingy from aboutV 1.0% to about 10.0% by weight of an iron-group metallic component, and at hydrocrack ing`conditions' including a temperature within the range of from about 200 F. to about 600 F.; and

(d) commingling the total etiluent from the hydrocracking step with said aromatic-containng charge stock as said previously hydrocracked product.

8. A process for converting an aromatic-containing hydnocarbonaceous charge stock boiling substantially at temperatures above the middle-distillate boiling range,

mixed therein with a previously hydrocracked product from said upper zone;

(b) reacting said charge stock and hydrogen at hydrogenation conditions selected to hydrogenate aromatic 23 into lower-boiling hydrocarbon products which comprises tho steps of:

(a) commingling said charge stock with a .previously hydrocraclced product and hydrogen, reacting said charge stock in contact with a non-siliceous, halogen 5 containing hydrogenation catalyst containing at least one metallic component from the platinum-group of the Periodic Table, and at hydrogenation conditions including a temperature above about 300' F., selected compounds without substantial conversion of said charge stock into lower-boiling hydrocarbons;

(c) separating from the resulting hydrogenated, sub-` stantially aromatic-free product efuent a hydrocarbon fraction having an initial boiling point of at least about 400' F.; t (d) reacting said hydrocarbon fraction and hydrogen, in said upper zone of hydrocracking catalyst and at (b) separating the resulting aromatic-free hydrohydrocracking conditions including a temperature genated product eiuent to provide a hydrogen-rich Y above about 200 P., and eommingling the resulting gaseous phase and a normally liquid hydrocarbon 15 total hydrocraclred product with said charge stock fraction having an initial boiling point of at least and hydrogen as aforesaid.` v about 400 F.; Y 1l. The process of claim 10 further characterized in (c) commingling said gaseous phase and said hydrothat said hydrogenation conditions include a temperature carbon fraction and reacting the same in contact with above about 300 F., selected to provide a maximum an alumina-silica hydrocraeking catalyst containing 20 hydrogenation catalyst temperature below about 650 F. from about 1.0% to about 10.0% by weight of an 12. The process of claim 10 further characterized in irongroup metallic component, and at hydrocrackthat said hydrogenation catalyst comprises alumina and at ing conditions including a temperature within the least one metallic component selected from the group conrange of from about 400 F. to about 800 F.; and sisting of the metals of the platinum-group and com- (d) commingling the total et'uent from the hydro- 25 pounds thereof.

cracking step with said aromatic-containing charge 13. The process of claim 10 further characterized in stock as said previously hydrocracked product. that sald hydrocraclting catalyst comprises at least one 9. The process of claim 8 further characterized in that metallic component selected from the group consisting of said hydrogenation catalyst comprises from about 0.01% the metals and compounds of Group VIII of the Periodic to about 5.0% by weight of platinum composited with 30 Table composited with an alumina-silica carrier material. alumina and from about 0.1% to about 1.0% by weight to hydrogenate aromatic compounds and to provide 10 a maximum hydrogenation catalyst temperature'less than about 650 F.;

gf halogen selected from the group of chlorine and Renten cned by he gamme,

nonne.

10. A process for converting a hydrocarbonaceous UNITED STATES PATENTS charge stock containing aromatic compounds into lower- 36 2,671,754 3/54 De Rosset et al 208-67 boiling hydrocarbon products which comprises the steps 2,971,901 2/61 Halik et al. 208-59 of: 3,008,895 11/61 Hansford et al 208-112 (a) passing a mixture of said 'charge stock and hydro- 3,023,158 2/62 Watkins 208-110 gen into a reaction chamber containing an upper 3,092,567 6/63 Kozlowski et al. 208-51 zone of an acidic hydrocracking-catalyst and a sepa- 40 3,132,086 5/64 Kelley et al. 208-112 rated lower zone of .a nonsiliceous hydrogenation catalyst, said mixture being introduced at a point ALPHONSOD-SULLWAN. Primary 510mm".

intermediate said upper and lower zones, and ad- 

5. A PROCESS FOR CONVERTING AN AROMATIC-CONTAINING HYDROCARBONACEOUS CHARGE STOCK INTO LOWER-BOILING HYDROCARBON PRODUCTS WHICH COMPRISES THE STEPS OF: (A) COMMINGLING SAID CHARGE STOCK WITH A PREVIOUSLY HYDROCRACKED PRODUCT AND HYDROGEN REACTING SAID CHARGE STOCK IN CONTACT WITH A NON-SILICEOUS HYDROGENATION CATALYST CONTAINING AT LEAST ONE METALLIC COMPONENT FROM THE PLATINUM-GROUP OF THE PERIODIC TABLE, AND AT HYDROGENATION CONDITIONS INCLUDING A TEMPERATURE FROM ABOUT 350* F. TO ABOUT 650* F. AND A LIQUID HOURLY SPACE VELOCITY OF FROM ABOUT 1.0 TO ABOUT 15.0 CORRELATED TO HYDROGENATE AROMATIC COMPOUNDS WITHOUT EFFECTING A SUBSTANTIAL DEGREE OF HYDROCRACKING; (B) SEPARATING THE RESULTING SUBSTANTIALLY AROMATIC-FREE HYDROGENATED PRODUCT EFFLUENT TO PROVIDE A HYDROGENRICH GASEOUS PHASE AND A NORMALLY LIQUID HYDROCARBON FRACTION HAVING AN INITIAL BOILING POINT OF AT LEAST ABOUT 400 F.; (C) COMMINGLING SAID GASEOUS PHASE AND SAID HYDROCARBON FRACTION AND REACTING THE SAME IN CONTACT WITH AN ALUMINA-SILICA HYDROCRACKING CATALYST CONTAINING AT LEAST ONE METALLIC COMPONENT FROM THE METALS AND COMPOUNDS OF GROUP VIII OF THE PERIODIC TABLE, AND AT HYDROCRACKING CONDITIONS INCLUDING A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 200* F. TO ABOUT 800* F.; AND (D) COMMINGLING THE TOTAL EFFLUENT FROM THE HYDROCRACKING STEP WITH SAID AROMATIC-CONTAINING CHARGE STOCK AS SAID PREVIOUSLY HYDROCRACKED PRODUCT. 